Ultra-high vacuum, taken as below 10⁻⁷ mbar, and in surface science usually below 10⁻⁹ mbar. At these pressures a freshly cleaned surface stays clean for hours instead of seconds, so UHV is the working range for surface analysis, particle accelerators and molecular beam epitaxy. Getting there demands CF metal seals, a bake-out at 150 to 250 °C, low-outgassing materials and capture pumps such as ion pumps and NEGs, and the residual gas ends up mostly hydrogen from the steel walls.
System's been UHV for a month, low 10 to the minus eleven on the B-A, so nobody touch that gate valve.
Below about 10⁻¹² mbar people start saying XHV, extreme high vacuum, and the gauges themselves become one of the bigger gas sources.
Also heard as
- ultra-high vacuum
- ultrahigh vacuum
Related terms
High vacuum
The range from about 10⁻³ down to 10⁻⁷ mbar, where molecules mostly hit the walls rather than each other.
Bake-out
Heating a vacuum system while pumping to drive off water and other adsorbed gas and lower the base pressure.
CF flange
All-metal flange that seals by biting knife edges into a soft copper gasket, the standard joint for UHV.
Ion pump
Capture pump that ionizes gas in a high-voltage magnetic discharge and buries the ions in titanium.
NEG
Non-evaporable getter: a porous alloy that pumps active gases once it has been activated by heating in vacuum.